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Penta Faq

n xntrx volvo

Dec 5, 2003
corinth, ms / los angeles
Volvo is a well diversified Company. Aside from the manufacture of Heavy trucks, they are also well known in the Marine world for their boat motors. Some Engines are re-badged Versions of Chevy and Ford Engines, but some are based on Volvos own engines. Due to boat motors being ran for several hours at high rpm's, many items in these motors have been upgraded internally. Most have also been mixed with the best of the volvo parts bin, and/or had penta specific parts added in the quest to add aditional hp without turbocharging (marine folks have a harder time finding good gas sometimes). I have compiled a list and info of models that are of interest to those on this site.
Happy hunting,


volvo factory info/ sales lit

-80MM stroke
-8v 1000160 head
-"A" cam,
-80MM stroke
-8v 1000531 head
-"A" cam,
-CR 9.8:1
Aq131 / aka 230, 275
-80MM stroke
-8v 1000531 head
-Single Carb
-"A" cam
- cast crankshaft
-80mm stroke
-8v 1000531 head
-Dual Carb
-"V" cam
-All Square Tooth Belt
-CR 9.7:1,
Aq151 = aka 250
-2.49l, or 151ci
-86MM stroke
-Forged crankshaft
-8v 1000531 head
-Dual Carb
-"V" cam
-CR 9.7:1. comp press 142-170psi
-Cast V pistons
-All Square Tooth T-Belt
-551.2 lbs
-max speed 5500 rpm
Aq171/ aka 251a(dohc)
-2.49L, 151.9ci
-86MM stroke
-16V Head
-Dual Carb
-"PZ" cam
-CR 9.7:1
-Cast V pistons
- Forged Crankshaft
-All Round Tooth T-Belt

All are carb, generally Solex. This is a good way to id the high performance motors. Single are budget (for a marine motor), dual are high performance.

Aq125, Aq140, Aq145 = b2x block
Aq131, Aq151, Aq171, Aq251 (dohc) = b230 block
Super Marine block which is very similar to the R block. It can be bored up to 99mm successfully.
No pentas came w/ squirters, they have the bolts/are machined for them in late ones though. They can be easily added to these motors.

Stoker/ crank info
The aq151 and aq171 had a 86mm stoke crank. This compares to normal Volvo Auto 80mm, giving them a 2.5 liter displacement. These crankshaft are direct replacements for b230's of the same era.
The letters after the Penta number are important. Stay away from the A. It had small mains and was based on the 9mm rods. Early Penta motors, just like early B230s, had less desirable bearings and bearing location, and rods. Blocks produced before 1988 used small mains and 9mm rods, 1988+ = 63mm mains and big rods.
Some penta cranks are forged (cast units are noted below). The forged crankshaft will have a thick parting line on the counter weights.
Breakdown by model
- Small
AQ131A, AQ131B (cast)
AQ151A, AQ151B
AQ171A, AQ171B
AQ131C, AQ131D (cast)
AQ151C, AQ151D
AQ171C, AQ171D
sp 230 (all) (cast)
sp 250 (all)
sp 251 DOHC (all)

Rod / Piston interchange
the AQ151 and AQ171 use the same 152MM long conn rods as the B230 engine, and use a 3MM shorter compression height (wrist pin to piston crown) to compensate for the longer stroke.
<table frame="hsides" rules="all" width="360"> <thead> <tr style="height: 2cm;"> <th title="Piston dimensions (mm) / Piston pin dimensions (mm)" colspan="2" align="center">

</th> <th title="Mounting of piston rings" align="center">

</th> <th title="Nominal diameter of cylinder" align="center">

</th> <th title="Piston article number" align="center">

</th></tr></thead> <tbody> <tr> <td align="center"> <table> <tbody> <tr> <td title="Compression height">Compression
</td> <td align="right">36,7</td></tr> <tr> <td title="Combustion chamber depth">Combustion Chamber Depth
</td> <td align="right">3,2</td></tr> <tr> <td title="Distance between bosses">Distance Between Bosses
</td> <td align="right">25</td></tr> <tr> <td title="Total length">Total Length
</td> <td align="right">61,7</td></tr> <tr> <td colspan="2">

</td></tr></tbody></table></td> <td align="center">Total Length
65</td> <td align="center"> <table> <tbody> <tr> <td title="Ring type: Rectangular ring">R</td> <td title="Height of ring">1,75</td> <td>Cr </td></tr> <tr> <td title="Ring type: Taper-faced Napier ring">NM</td> <td title="Height of ring">1,75</td> <td>
</td></tr> <tr> <td title="Ring type: Coil spring loaded slotted oil control ring">SSF</td> <td title="Height of ring">3,5</td> <td>
</td></tr></tbody></table></td> <td title="Nominal diameter of cylinder" align="center">96,01</td> <td align="center">037 03 00
96 V 18</td></tr></tbody></table>

the V-cam has 11.37 max lift inlet and outlet and has an overlap of apr. 12 degree. lobe separation (108.5)
For more 8v camshaft info click here
Aq171 pz cams, the lobes on the PZ cams are 0.7mm taller from base to peak then the stock cams and about 0.5mm wider across. For a PZ review click here. PZ's are a drop in for 16v cars also.

Cylinder Heads
<table border="0" width="740"> <tbody><tr><td class="sheetText" width="610">Cylinder heads for petrol engines consists of:
Cylinder head, intake and exhaust valves, valve springs, washers and lock. For B21, B23, B230 and B250 engines camshaft is also included.

</td> </tr> <tr> <td width="610">
<table border="1" bordercolor="#8e95db" cellpadding="2" cellspacing="0" width="100%"> <tbody><tr> <td class="sheetTH" align="left" valign="top" width="60">Pos no.</td> <td class="sheetTH" align="left" valign="top" width="80">Part no.</td> <td class="sheetTH" align="left" valign="top">Engines/Drives</td> <td class="sheetTH" align="left" valign="top">Spare part no.</td> </tr> <tr> <td class="sheetTD1" align="left" valign="top">90.1</td> <td class="sheetTD1" align="left" valign="top">3803012</td> <td class="sheetTD1" align="left" valign="top">AQ115A, AQ130, BB115A, MB20A</td> <td class="sheetTD1" align="left" valign="top">831656</td></tr> <tr> <td class="sheetTD2" align="left" valign="top">90.1</td> <td class="sheetTD2" align="left" valign="top">3803018
1) </td> <td class="sheetTD2" align="left" valign="top">AQ120B, AQ125A</td> <td class="sheetTD2" align="left" valign="top">463630</td></tr> <tr> <td class="sheetTD1" align="left" valign="top">90.1</td> <td class="sheetTD1" align="left" valign="top">3803025
2) </td> <td class="sheetTD1" align="left" valign="top">AQ140A, BB140A</td> <td class="sheetTD1" align="left" valign="top">463630</td></tr> <tr> <td class="sheetTD2" align="left" valign="top">90.1</td> <td class="sheetTD2" align="left" valign="top">3803226
3) </td> <td class="sheetTD2" align="left" valign="top">AQ145A, BB145A</td> <td class="sheetTD2" align="left" valign="top">857532</td></tr> <tr> <td class="sheetTD1" align="left" valign="top">90.1</td> <td class="sheetTD1" align="left" valign="top">3803166
3) </td> <td class="sheetTD1" align="left" valign="top">AQ145B</td> <td class="sheetTD1" align="left" valign="top">1346408</td></tr> <tr> <td class="sheetTD2" align="left" valign="top">90.1</td> <td class="sheetTD2" align="left" valign="top">3803167
4) </td> <td class="sheetTD2" align="left" valign="top">230/SP, AQ125B, AQ131</td> <td class="sheetTD2" align="left" valign="top">1346408</td></tr> <tr> <td class="sheetTD1" align="left" valign="top">90.1</td> <td class="sheetTD1" align="left" valign="top">3803168
5) </td> <td class="sheetTD1" align="left" valign="top">250/SP, AQ151</td> <td class="sheetTD1" align="left" valign="top">1346408</td></tr> <tr> <td class="sheetTD2" align="left" valign="top">90.1</td> <td class="sheetTD2" align="left" valign="top">3803201
6) </td> <td class="sheetTD2" align="left" valign="top">AQ171 DOHC</td> <td class="sheetTD2" align="left" valign="top">856528</td></tr> <tr> <td class="sheetTD1" align="left" valign="top">90.1</td> <td class="sheetTD1" align="left" valign="top">3803201</td> <td class="sheetTD1" align="left" valign="top">251DOHC</td> <td class="sheetTD1" align="left" valign="top">856097</td></tr> </tbody></table>
A camshaft.
D camshaft.
K camshaft.
A camshaft.
V camshaft.
Piston kit 876236, 4 pcs. are required.
</td> </tr> <tr> <td class="sheetText" width="610">
</td></tr></tbody> </table>
B23 based blocks use these mounts Penta's mount low and on the drivers side. 50 amp. These mounts can be used on car red blocks, using stock holes. Most i've seen, are GM style alts, w/12 and 6 clocking. The B230 based ones have a small alternator mount built into the motor mount bracket.

Condition advisory

Watch out for used volvo boat engines. Salt water likes to eat and corrode everything in it's path. try to get a boat engine/ parts that only saw fresh water use.

While these engines use a fresh water cooling system (a seperate cooling system from the sea cooling system) the salt water/ sea water still exits through the exhaust manifold. this causes corrosion on the #4 ex port, which is why these engines have round, sleeved exhaust ports there.

The Pentas use a small ID plate on the starter section of the block


the first entry (shown as 250b on the example) is the engine designation
the second entry (next to the last) is the product number
next line, (first ten digits) Serial number
the last 5, basic engine serial number

there also is the product designation, on the block. Its located right under the head, drivers (in a car) side.

Date code on the block is the same as auto units. just to the rear and lower than the oil filter. its a XXXXXX. the first two are the year of manufacture, ie 93 = 1993 etc. This plate will be obscured by the oil cooler on the dual carb models.

That oil cooler (click here for pic) will be a tip if loking for a 2.5l short block. It was only on dual carb models. The oil filter bolt will be extra long for this if its been removed. All 2.5l blocks are still stamped "b230" on the passenger (in a car) side.

The easy visual differences between the b23 and b230 based engines:
#1 The harmonic damper on the front. It will be a solid unit on b23/b21 engines. On b230 based engines it will be a 2 pc unit, connected by a rubber insulator inside.
#2 The valve cover: on b23/b21 based units it will be flat across the back. On b230 based units, it will have a half circle for the dizzy on autos.
*Note*, some late b23 based ones do have the late style valve cover, use #1 whenever possible.

Fyi, the late engines are manufactured with two different product designations. During the 1989 Volvo Penta Begain designating engines based on their cylinder diplacement according to the ISO norm 8665. The designation is listed above in the engine descriptions. ie, a aq171 is a 251 from 1989 on. Since these are the models you'll most likely be interested in, use these in your search criteria.
Parts specs and #'s
*Warning* Volvo Penta Parts are expensive. These engines are heavily prized in both the automotive and marine world. You'll also find that anything in the marine world is extremely over-priced.

parts catalog

aq171 parts
belt =
-146 teeth
-timming marks on belt
-non-spring loaded, vw style
cam (in) =
cam (ex) =
shimed lifters = 1317798-5
aq171a crank =
-main bearing dia, 55mm
aq171c crank
-main bearing dia
piston kit std
-height pin to top, 36.7mm
-overall height, 61.7mm
-all light alloy
piston kit .030
piston kit .060
block dizzy plug
timming pointer for aux shaft (aq171 specific)
tensioner bolt
tensioner spacers/washers
-955895-8 & 855795-1
drivers side alt mount
valve (in)
valve (ex)
spark plug
-.276" gap
Last edited:

The Aspirator

It's a girl!
Apr 7, 2003
Vinemount, Ontario CANADA
Great writeup!

Yes, be vary cautious about salt water marine engines, the heads get very corroded and sometimes become basically junk. I got an AQ125 engine with a 531 head that looked fine from the outside, but the exhaust manifold was STUCK to the head and broke peices off the head when we finally hammered it off. The exhaust ports of the head were chewed away, making it junk. And this is what the block looked like when we took the head off:
Click for picture
Honest, it looked fine on the outside when I got it! Hahahaha. Also, the marine bellhousing seems to be stuck on there as well, cause I can't for the life of me pry if off.


n xntrx volvo

Dec 5, 2003
corinth, ms / los angeles
davidmacq said:
Hard to tell from that above, but is super marine=aq251??
not that i'm aware of, but i'm not aware of much.

john, your aq125 has a 531? the info i found was 160, along w/ one that i've seen. Whats the letter designation? maybe there was a transition in there, cuz the lit lists the same power, for 125 and 131.
i'm lost,

The Aspirator

It's a girl!
Apr 7, 2003
Vinemount, Ontario CANADA
I've got two Aq125 engines, one's actually in my brothers car right now. One is an AQ125A the other is a 125B I think. They both had A-cams. One had a 160 head, the other had a 531 head. I forget which was which. John


cutting, welding, bashing
Mar 3, 2003
Cheltenham, UK
Hi John,
I can guarantee that the siezed bellhousing will be the spline's on the flywheel plate and the gearbox(propeller housing).
As boat's don't have clutches the there is a solid plate with a clutch like centre ie splined hole, into this hole is the main shaft for the gearbox/prop housing this was absolutley siezed solid on the AQ171 I disassembled.
As I was only interested in the rotating assembly and the head I removed the was able to drive a chisel between the bellhousing and block(bolt's removed obviously) and had to work it from side to side for about half an hour increasing the chisel/crowbar each time.
It took 2 of us to do it, applying equal pressure to each side of the bell housing.
It wasn't fun!!! but you'll get there!
Last edited:

The Aspirator

It's a girl!
Apr 7, 2003
Vinemount, Ontario CANADA
Thanks for the tip, I wasn't really sure what it was like inside the bellhousing. That makes a lot of sense. I really hold no value in the block cause it's total crap. Although one day I might take off the oil pan and check to see how the crank and rods are doing. On the side of this AQ125 block it says B230, so I'm guessing it's got either 9mm or 13mm rods inside. Whereas the block on my brothers car which is also an AQ125 (just a different letter designation) definately had M-rods and a forged crank, so it's B23 based. It didn't say B230 on the side.



Board Member
Nov 13, 2002
Two Up, Two Down
first off...aaron, thanks so much for compiling this list!

n xntrx volvo said:
volvo factory info/ sales lit
parts catalog

Aq151 = aka 250 2.5L (86MM stroke) 8v with 1000531 head and "V" cam CR 9.8:1. 146hp

Crank interchange
aq151 and 171 are 86mm (+6mm) stroke, verses the stock 2.3l 80mm (+6mm), direct fit for b230 blocks.
All penta cranks are forged.

Rod interchange
the AQ151 and AQ171 use the same 152MM long conn rods as the B230 engine, and use a 3MM shorter compression height (wrist pin to piston crown) to compensate for the longer stroke.
so given this info, will the 151 crank/rods/slugs and head all swap right into any b230 block? like...if i get a later AQ, with the updated bearings and stuff, and throw it into a later B230 block, it'll work well and still run 9.8:1 compression? thats about the upper limit of compression i feel comfortable running on a boosted motor, and if the above is true, that means i have less to do before my AQ+T project is complete!


New member
Jan 24, 2003
Has anyone ever offset ground a penta crank off a 151/171 to get even more stroke? Maybe 2.7 liters(not +), not sure if the lower of the block can be modded for clearence. Just something I was wondering about.

Magnum TE

Broke another B230F+T
300+ Club
Nov 12, 2002
Santa Rosa Ca
can someone post part numbers in this thread.... for pistons and roda and the like. They didnt have aq171 pistons in tha parts catalogue.


New member
Oct 31, 2004
Glasgow Scotland
AQ171C or AQ251A

Has anyone come across the ignition control module (coil and amplifier) for either of the above engines in their marine environment?

Do you have it ?

Do you need it ?

If you don't, could you throw it in my direction please.

Happy to pay for the part and shipping.


Bored Member
Feb 17, 2003
Clarksville, TN
"Rod / Piston interchange
the AQ151 and AQ171 use the same 152MM long conn rods as the B230 engine, and use a 3MM shorter compression height (wrist pin to piston crown) to compensate for the longer stroke. "

Hmm, I'm wondering it compensates for a longer stroke? but the longer stroke increases output from 2.3 to 2.5. Does this mean there is a way to rework the combination of parts to achieve more than 2.5L? Compression height sounds like it may just raise compression. Will be very interesting when some of these 2.5L projects finish and we see how things turn out.

On a side note. Saw a block without crank, cam n pistons, etc selling for $700 starting price on ebay. Wonder where those parts went? haha Also a whole AQ171 engine with asking price of $2200 and saw something that showed a 2.5L crank new would be around $1100. Wow, gotta be some old parts engines around.